The use of the exploratory/development mechanism was chosen to allow for the development of methods to examine the hormonal pathway for priming paternal care behaviors in biparental males. The common marmoset, Callithrix jacchus, is the ideal model for studying hormonal activation of male parental care due to their active participation in infant care from the first day of birth. Fathers are highly responsive to infant cues, but show between male variability as do human fathers. Parentally naive males are much less responsive to infant cues than experienced males, suggesting there is an experience and hormonal influence on paternal behavior. Specific Aim 1 will test paternally experienced adult male marmosets for their infant responsiveness to an infant or control stimulus by steroid treatment with either estradiol or testosterone or vehicle. We will examine changes in prolactin, oxytocin, vasopressin and dopamine with steroid stimulation in both central and peripheral samples. Specific Aim 2 will examine the communication between the anterior and posterior pituitary through culturing both intact and separated pituitaries before and after steroid challenges. Changes in levels of pituitary hormones will be compared to in vivo changes found in Specific Aim 1. Specific Aim 3 will test paternally naive males for their infant responsiveness by steroid treatment, as in Specific Aim 1 and for their pituitary responses as in Specific Aim 2. Inexperienced male's behavioral and hormonal responses will be compared to experienced males and pituitary responses to steroid treatment will be compared with the experienced males. Marmosets are one of the few mammalian species whose social organization/family structure bears resemblance to that of humans. Poor parenting results in a number of pyschosocial disorders, such as neglect and abuse, which confound human health. Understanding the mechanisms of paternal care in a bi-parental species will lay the foundation for development of treatments to create positive parenting. PUBLIC HEALTH RELEVANCE: This project seeks to understand the factors underlying quality paternal care in males. With poor parenting or parental absence, there are a number of psychosocial disorders that confound human health. Fathers can contribute significantly to the positive outcome of infant and child development.